1. Field of the Invention
The present invention relates to non-volatile memory devices. More particularly, the present invention relates to non-volatile memory devices including a material whose resistance varies according to an applied voltage.
2. Description of the Related Art
Non-volatile memory devices are generally divided into floating gate non-volatile memory devices and charge trapping non-volatile memory devices.
A unit cell of the floating gate type non-volatile memory device usually includes a tunnel oxide layer, a floating gate, a dielectric layer and a control gate that are formed on the semiconductor substrate. Charges may be injected into or emitted from the floating gate so that information may be stored in the floating gate non-volatile memory device.
A unit cell of the charge trapping non-volatile memory device usually includes a tunnel insulation layer, a charge trapping layer, a blocking insulation layer and an electrode that are formed on a semiconductor substrate. The tunnel insulation layer and the blocking insulation layer typically include a silicon oxide. The charge trapping layer typically includes a silicon nitride, and the electrode usually includes doped poly-silicon. Charges may be stored into or emitted from the charge trapping layer disposed between the electrode and the semiconductor substrate so that programming and erasing may be performed.
As described above, data may be programmed or erased by using charges in the unit cell of the floating gate and the charge trapping non-volatile memory devices; however, stored charges in the floating gate or the charge trapping layer may move from the floating gate or the charge trapping layer due to cell to cell interference between adjacent cells in the above non-volatile memory devices, and thus operation failures may occur.
Additionally, the number of the charges stored in the floating gate or the charge trapping layer is very small because the non-volatile memory device may be highly integrated. Accordingly, data stored in a cell of the non-volatile memory device may be difficult to distinguish from that in another cell, and data distribution in the cells may not be good.